Pulsed-energy detonation system for electro explosive devices

ABSTRACT

The invention comprises a technique and apparatus for destroying electro-explosive devices such as underwater mines by subjecting them to intense electromagnetic radiated fields. A unique arrangement of a capacitor which discharges into a resonant circuit including an antenna is used to generate the high energy field by pulse techniques.

EJ11011 States atent 1191 1 1111 3,707,913 Lee 14 1 Jan. 2, 1973 1541PULSED-ENERGY DETONATION 3,230,506 1/1966 116110116 ..340/4 E x SYSTEMFOR ELECTRO EXPLOSIVE 2,397,209 3/1946 50118810111111 ..89/1 A x DEVICES2,411,787 11/1946 Hammond, Jr ..102/8 2,937,611 5/1960 50118816111111 eta1. ..114/221 Inventor: Willis 1879 Marlowe Street, 3,040,658 6/1962Maltby ..102/19.2 x

Thousand Oaks, Calif. 91360 3,060,883 10/1962 Herbst et a1. ..102/10[22] Filed: July 1969 Primary Examiner-Samuel W. Engle [21] Appl. No.1849, 56 Attorney-J. C. Warfield, Jr., George J. Rubens and John W.McLaren [52] 11.8. C1. ..102/18,114/221R, 340/4 R 511 1111.01 ..F42b22/30 [571 ABSTRACT Field of Search 1 The invention comprises atechnique and apparatus 114/221, 2155;340/12, 4 for destroyingeiectro-explosive devices such as underwater mines by subjecting them tointense elec- [56] References Cited tromagnetic radiated fields. Aunique arrangement of UNITED STATES PATENTS a capacitor which dischargesinto a resonant circuit including an antenna is used to generate thehigh energy 2,985,837 5/1961 Ruehlemann et a1 ..l02/70.2 X field bypulse techniques. 3,105,170 9/1963 Palmer ..315/183 3,229,158 1/1966Jensen ..320/1 X 1 Claim, 1 Drawing Figure [0 ,2 [/2 POWER SUPPLY a:CAPACITOR a MATCHING V SWlTCH V NETWORK l5 /4 j REASONANT CIRCUIT c ANDANTENNA PMENTEDJAN 2191s 3.707.913

POWER SUPPLY CAPACITOR MATCHING SW'TCH T NETWORK REASONANT ClRCUIT ANDANTENNA INVENTOR.

WLL/S L. LEE

BY v

AITORNE Y5 PULSED-ENERGY DETONATION SYSTEM FOR ELECTRO EXPLOSIVE DEVICESSTATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION It has been known for some time that squibs,electroexplosive devices (EEDS), some booster charges, and otherordnance materials are susceptible to damage from radio frequencyfields. A great effort has been extended to analyze and determine theexact nature of these effects. This effort has been expandedsignificantly since many previous mishaps which had been accredited toother causes have now been found to be due to radio frequency hazards.

One method which has been attempted to remove radio frequency hazards isradio silence. Another method attempted is the use of desensitized EEDS,such as low impedance (1 amp, 1 watt), squibs. Neither of these methodshave appreciably met the desired criteria of safety.

If high power radio frequency or very low frequency radio transmitterswere available to develop high intensity electromagnetic fields inwater, for example, the probability of mine destruction would be verygood, especially in the case where long electrical leads are connectedto the mines. However, when calculations are made for losses due to theantennas and water, it becomes apparent that a transmitter of the typerequired using continuous transmission operation would be impractical toconstruct. Furthermore such a transmitter would not be capable of mobileoperation. If instead of attempting continuous operation, pulsedenergytechniques are utilized, the required transmitter powers can beobtained.

SUMMARY OF THE INVENTION A pulsed-energy detonation system forelectro-explosive devices is disclosed. According to the concept of theinvention, electro-explosive devices are detonated by subjecting them tointense electromagnetic radiated fields. A capacitor is discharged intoa resonant circuit including an underwater antenna to generate thehigh-energy field by pulse techniques. The system can develophigh-energy radio frequency pulses of, for example, l to watts yieldinga field strength range of 30,000 watts/meter to 250 watts/meter" atdistances of fifteen to thirty meters in brackish waters.

STATEMENT OF THE OBJECTS OF THE INVENTION An object of the presentinvention is to provide a pulsed-energy detonation system which can beused against electro-explosive devices.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing wherein:

BRIEF DESCRIPTION OF THE DRAWINGS The FIGURE is a schematic drawing ofthe pulsedenergy detonation system of the present invention wherein theelectro-explosive device comprises an underwater mine.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, an Ac or DCpower supply 10 is connected by means of an electrical lead 11 to avariable capacitor 12. The capacitor operates to store electrical energyand to discharge such energy to the conventional resonant circuit andunderwater antenna 18 shown immersed in a liquid 19. A switch 14 isconnected in series with the capacitor 12 by means of an electrical lead13. Switch 14 functions to inject the stored electrical energy fromcapacitor 12 into the liquid 19 for propagation therein. Switch 14 isconnected by means of an electrical lead 15 to a conventional matchingnetwork. The output of the matching network 16 is connected by means ofan electrical lead 17 to the conventional resonant circuit andunderwater antenna 18.

In operation, a source of electrical energy such as AC or DC powersupply 10 charges capacitor 12. When switch 14 is closed, the energystored in the capacitor is discharged to the underwater antenna 18. Theelectrical energy received at the antenna 18 is then converted intoelectromagnetic energy. This electromagnetic energy is then propagatedthrough the medium 19 in which an underwater mine, for example, islocated.

The capacitance of the capacitor 12 may be varied to change the strengthof the electrical pulses as desired. Also frequency modulation maytypically be accomplished by controlling the interval between pulsessuch as by controlling the frequency of the basic power supply 10.

The system of the invention can be constructed to develop high-energyradio frequency pulses of, for example, 10 to 10 watts yielding fieldstrengths of 30,000 watts/meter to 250 watts/meter at distances of from15 to 30 meters in brackish waters. 100 watts/meters has beenestablished as being hazardous for even the safest EEDS since manydetonate in fields of less than milliwatts/meter.

By using pulsed-energy techniques, transmitter powers of from 10 to 10watts are possible. For example, a 30,000 joule system could be built todeliver 3 X 10 watts which would give a spherical radiated field atthirty meters of approximately 250 watts/meter? By way of example, a 60microfarad capacitor with a peak voltage rating of 9 KV could be used inthis system. In order to acquire a 500 joule system, the capacitor wouldbe charged to 8.2 KV to offset the 25 percent dump efficiency of thecapacitor switch as its worst practical case. If the system impedance ismatched and all desired design criteria are met, such a system will ringat or above KC. For a ringing frequency of 100 KC the pulse power willbe:

W=(5 X 10joules)/l0"" second= 5 X10 watts.

If a 40 db antenna attenuation is assumed, for example, the poweravailable from the load, W would be reduced by a factor of 100 (40 db)and hence would become:

The above calculations are based on the use of the half-wave antennasystem approximately fifteen meters long and having a worst case loss of40 db.

Assuming a target range of 5 meters, the power density would be reducedby spherical dispersion, if no antenna directivity is considered, to:

P W/41r R (5 X lO )/41-r (5) 1.6 X lo lmeter 2 where W is the power inwatts' available from the source, and R is the range in meters.

If the liquid in which the antenna is submerged comprises brackishwater, it will offer an attenuation of 1 db per meter and therefore, fora five meter range, the attenuation would be 5 db or a reduction factorof 3.16. This attenuation would further reduce power density at fivemeters to:

[n a typical case, this power density would probably be more thannecessary and thus as much as, for example, a 7 meter range could beused.

Calculations for a seven meter range give a value of: P 163 watts/meterwhich is well above the established 100 watts/meter hazardous level.

Seven meters, for example, represents a distance from the antenna systemof approximately a quarter wavelength for the chosen frequency. If asmaller system were chosen, any variations in losses could place the EEDso close to the antenna as to yield the system impractical by damagingthe antenna.

As a secondary check, the energy density at seven meters is calculatedas follows:

Since the attenuation of water for seven meters is approximately 7 db ora reduction factor of five, the final field density is equal to:

B 8.17 X l /5 1.63 millijoules/meter.

If this amount of energy were induced into an average EED, theprobability of detonation would be greater than 99.7 percent accordingto known information. An energy of 1.79 millijoules induced into the EEDwould yield a probability greater than 99.993 percent.

Thus, it can be seen that a new and novel method of detonatingunderwater mines by subjecting them to intense electromagnetic fieldshas been disclosed. The unique arrangement of a capacitor whichdischarges into a resonant circuit including an underwater antenna isused to generate the high fields by pulse techniques. If conventional RFgenerating equipment were used, the space considerations would beimpractical for generating signals having the power necessary. By usingpulse energy techniques from a charged capacitor, the system becomesentirely feasible. By selectively triggering a switch, the capacitorenergy is dumped into a resonant CjlCUlt including an an enna. Theresultant electromagnetic signal from the antenna is propagated throughthewater.

Although the preferred embodiment is directed towards the detonation ofunderwater ordnance, it is obvious that the inventive concept ofdetonating electro-explosive devices is equally applicable to suchdevices located in air or underground.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for detonating electro-explosive devices which aresusceptible to detonation by intense electromagnetic radiated fieldscomprising:

a. a source of electrical energy;

b. said source including variable capacitor means for storing saidelectrical energy;

0. switch means in series with said variable capacitor means;

d. resonant circuit means including antenna means located in thevicinity of the devices which are to be detonated;

e. said resonant circuit means being connected to said source ofelectrical energy and said switch means by a matching network;

f. said switch means being operable to discharge the stored energy insaid variable capacitor means to said resonant circuit means to therebygenerate pulsed intense electromagnetic fields.

1. Apparatus for detonating electro-explosive devices which aresusceptible to detonation by intense electromagnetic radiated fieldscomprising: a. a source of electrical energy; b. said source includingvariable capacitor means for storing said electrical energy; c. switchmeans in series with said variable capacitor means; d. resonant circuitmeans including antenna means located in the vicinity of the deviceswhich are to be detonated; e. said resonant circuit means beingconnected to said source of electrical energy and said switch means by amatching network; f. said switch means being operable to discharge thestored energy in said variable capacitor means to said resonant circuitmeans to thereby generate pulsed intense electromagnetic fields.